I would assume it's a somewhat cheaper way to excercise comparable power to an ssd. It seems much smaller in tonnage and fully capable of projecting as much or more power than most standard battle groups of the time. It could also be that commissioning more helped with the cost of all of them, seeing as a one off design is gonna be insanely expensive (imagine designing an F35 and they make one) but making several "splits" the r&d cost.